Composite superconductor

ABSTRACT

A hollow, elongated support, adapted to have a cooling medium circulating therethrough, has a plurality of stabilized superconductor assemblies spirally wrapped therearound, with a pitch of 1 to 30 cm. per winding; additionally, preferably, a second layer of windings of nonsuperconductive wire with a pitch of about half of the pitch of the superconductor assemblies is wrapped around the outside of the spiralled superconductor assemblies. A good heat-conductive, nonmagnetizable bonding medium bonds the stabilized superconductor assembly and, if used, the layer of wires of nonsuperconductive material to the support tube. In the method of manufacture, lengths of hollow longitudinal support tubes are joined to form a continuous fluidtight tube to which the superconductor assembly wires are first applied, then, if desired, the nonsuperconductive wires are wrapped therearound with a direction of twist opposite to that of the superconductor wires, the wires being placed closely adjacent each other so that, upon immersion into a melt of good heatconductive, nonmagnetizable material, the fluid material will flow by capillary action in the interstices between the wires to form a composite, encapsulated whole.

United States Patent Schaetti [54] COMPOSITE SUPERCONDUCTOR [72] Inventor: Norbert Schaetti, Glattbrugg, Switzerland [73] Assignee: Maschinentabrik Oerlikon, Zurich, Switzerland [22] Filed: June 8, 1970 [21 Appl. No.: 43,992

[30] Foreign Application Priority Data July 8, 1969 Switzerland ..10516/69 [52] [1.8. CI ..174/15 C, 174/27, 174/126 CP, 174/128 [51] Int. Cl. ..Hlb 7/34 [58] FieldofSearch ..l74/15C,D1G.6, 126 CP, 128, 174/27; 335/216 [56] References Cited UNlTED STATES PATENTS 3,428,926 2/1969 Bogner et a1 ..335/216 3,218,693 11/1965 Allen et al.... ...174/D1G. 6 3,504,105 3/1970 Bogner et al.. 174/ 126 3,502,789 3/1970 Barber et al. 174/126 X 3,514,850 6/1970 Barber et al. l74/DIG. 6 3,527,873 9/1970 Brechna et a1... ..l74/15 3,529,071 9/1970 Kafka ..174/l 3,472,944 10/1969 Morton et a1. 1 74/ 128 X FOREIGN PATENTS OR APPLICATIONS 1,463,138 11/1966 France ..174/DlG. 6

[ Feb. 15, 1972 1,505,605 1 H1967 France l 74/DIG. 6

Primary Examiner-Laramie E. Askin Assistant Examiner-A. T. Grimley Attorney-Flynn & Frishauf [57] ABSTRACT A hollow, elongated support, adapted to have a cooling medium circulating therethrough, has a plurality of stabilized super-conductor assemblies spirally wrapped therearound', with a pitch of l to cm. per winding; additionally, preferably, a second layer of windings of nonsuperconductiye wire with a pitch of about half of the pitch of the superconductor assemblies is wrapped around the outside of the spiralled superconductor assemblies. A good heat-conductive, nonmagnetizable bonding medium bonds the stabilized superconductor assembly and, if used, the layer of wires of nonsuperconductive material to the support tube. in the method of manufacture, lengths of hollow longitudinal support tubes are joined to form a continuous fluidtight tube to which the superconductor assembly wires are first applied, then, if desired, the nonsuperconductive wires are wrapped therearound with a direction of twist opposite to that of the superconductor wires, the wires being placed closely adjacent each other so that, upon immersion into a melt of good heat-conductive, nonmagnetizable material, the fluid material will flow by capillary action in the interstices between the wires to form a composite, encapsulated whole.

6 Claims, 1 Drawing Figure COMPOSITE SUPERCONDUCTOR The present invention relates to composite superconductors and to a method of their manufacture.

It has previously been'proposed to form superconductors of hollow tubes and circulate the cooling medium in the interior of the tubes under pressure. Stabilized superconductors have been proposed in which an assembly is provided consisting of a normally conductive material, such as copper, in which single filaments of superconductive material are embedded. The copper, if used, may be plated on the single filaments or the filaments may be embedded in the copper by means of a cold working process. These known, stabilized superconductor tubes, and particularly if they have a fairly substantial cross section, have the disadvantage that, when ordinary drawing processes are to be used, their length is limited to a maximum of about 50 meters. Since, however, frequently superconductors of substantially greater length are necessary, numerous joints and junctions are required which cause mechanical as well as electrical problems.

A superconductor may be made in which a normally conductive support material, which is hollow, has stabilized superconductors applied at the outer surface thereof, the stabilized superconductors being in ribbon form. Such a composite superconductor assembly has the advantage that the number of joints between the superconductive bands or tapes can be substantially reduced, so that the composite superconductor assembly will have high mechanical strength and that coils of a relatively small radius may be manufactured therefrom. Additionally, the manufacturing costs are comparatively low and the manufacturing processes are relatively simple. During the manufacture, a support is first provided by joining together predetermined lengths of support tubes and then the tapes of superconductive material are applied to the outer surface of the support tube by means ofa bonding layer.

Single filamentary superconductors which are parallel to the axis of the support tube cause eddy currents which can become substantial. These eddy currents give rise to an undesired magnetic field which is additional to any magnetic field desired to be applied to the superconductor. The strength of this additional magnetic field is not controllable. The value of the eddy currents themselves depends on the rate of change of the magnetic field, that is of the speed with which flux cuts the windings; the eddy currents may have a decay time which may be in the order of 1,000 hours-that is, a long time. The magnetic fields, due to the eddy currents, may have a field strength of several percent of the desired magnetic field; and after the magnetic field has been discontinued, remanent fields in the order of several thousand Gauss may remain over a substantial period of time.

For the foregoing reasons it is not possible to use superconductive magnets of the above type in precision measurements,

a disadvantage which arises particularly when such superconductors are to be used in large bubble chambers.

It is an object of the present invention to provide a composite superconductor, anda method of its manufacture, in which the above disadvantages are avoided.

SUBJECT MATTER OF THE PRESENT INVENTION Rather than arranging superconductor assemblies parallel to the axis of the support, the superconductor assemblies are helically, that is' spirally applied to the support through which the cooling medium flows. A good heat-conductive, nonmagnetizable bonding materialinterconnects these spirally applied superconductors to the outer surface of the support.

The helical twist of the individual superconductor assemblies greatly decreases, and may completely avoid the difficulties previously experienced with hollow composite superconductors.

According to a preferred form, the bonding material comprises a tin alloy, or pure indium; the melting temperature should not be over 320 C. In a preferred form, the composite superconductor is formed of a plurality of layers; first, a layer directly applied to the support tube formed entirely, or largely of superconductor assemblies and, thereabove, a second layer of wires having a direction of twist opposite to that of the first layer, and formed of wires of normally conductive material, such as copper. I

The wires of the first layer, and also of the second, if used, are preferably placed close to each other so that only small spaces will be left therebetween so that when the composite support and the layer, or layers of wire are dipped into a melt of bonding material, the bonding material will flow between the wires to totally surround the wires and support, and encapsulate the wires and support. This How will be by capillary action. If it is desired to form the superconductor with a square cross section, then a circular support may be first provided on which the superconductor assemblies are applied and the entire, composite unit is then deformed in such a manner that the desired and square, or rectangular cross section is obtained.

The invention will be described by way of example with reference to the accompanying drawing, wherein the single FIGURE illustrates a cross-sectional view of a composite superconductor in accordance with the present invention.

An elongated, hollow support 1, for example of copper, or of other normally electrically conductive material has stabilized superconductor assemblies 2 applied to the outside surface thereof. A cooling medium may be circulated through the hollow interior of the support 1. The superconductor assemblies 2 consist of single filaments 6, at least two, and preferably four (as shown) per assembly, surrounded by copper so that they are, inherently, stabilized. The materials of filament 6 may be alloys of titanium-niobium or niobium-zirconium. The layers of superconductor assemblies 2 are applied in helically progressing, spiral form with a pitch of, for example, 30 cm. per spiral turn. Wires 3 of nonsuperconductive material, for example copper, may be interposed in the layer ofsuperconductor assemblies, and spiralled therewith.

The first layer is covered by a second layer of wires 4. likewise helically spiralled but wound in a spiralling direction which is opposite to the direction of twist of the first layer, that is of wires 2, 3. The pitch of the wires of layer 4, which are of nonsuperconductive material such as copper is, for example, 15 cm. per twist. The support 1, the first layer of wires 2. 3, and the second layer ofwire 4 are securely bonded together by a bonding material 5, for example a tin-silver solder. The second layer of wires 4 is a protection against mechanical damage.

The pitch of the superconductor assemblies itself is not critical. Even a pitch of from to 300 cm. per twist accelerates the decay of the undesired eddy currents, so that they will be attenuated after several hours upon stationary operation of the magnet. If a pitch of several centimeters is selected, that is in the range of from 1 to 30 cm. per turn, then the formation of eddy currents can be entirely inhibited.

The composite superconductor is manufactured by first forming an elongated support 1 from single lengths of a predetermined length, for example 1,000 m., having a circular cross section. These single lengths are welded together to be fluidtight. Thereafter, a first layer of wires formed of superconductor assemblies 2 and, if desired, wires 3, is spirally twisted about the support 1. Thereafter, the second layer of wires 4 is spirally twisted thereover, with a direction of twist oppositeto that of the first layer, and with a pitch which may, for example, be half the pitch of the first layer, The composite is then pressed into the desired shape, for example of square or rectangular cross section. The wires 2, 3, and the wires 4 of the second layer are interconnected and bonded with each other, and with the support 1 by the bonding material 5, for example by dipping the superconductor into a melt of the bonding material, or carrying it through a bath of molten bonding material, for a period of time sufficiently long to permit the bonding material to be applied by capillary flow and completely surround and encapsulate the layers of wire, interconnecting the wires among themselves and to the support 1.

Bonding material 5, in addition to bonding the wires, further should have good heat transmi'ssibility to ensure good heat transfer between the wires and the support. Additionally, it should be electrically conductive, but nonmagnetic. Due to the nature of the superconductive material in the superconductor assemblies, the bonding material should have a melting temperature not above 320 C. It is desirable that the bonding material, when at a temperature of 42 K., has an electrical specific resistivity of atmost 1'10 ohm-cm. and a heat conductivity of at least 0.4 w./cm. K.

The superconductors in accordance with the present invention can be made by the method, as described, easily in substantial length, withoutrequiring manufacture of a special internal connection of the individual superconductive filaments 6. The superconductor wire assemblies 2 can readily be made in lengths of over 1,000 m. without causing undesirable high eddy currents therein during operation; such long superconductor assemblies can then readily be applied to long support tubes.

lclaim:

1. Composite superconductor having at least one stabilized superconductor assembly and a hollow, elongated support adapted to have cooling medium circulating therethrough, comprising a plurality of wires spirally wound about said support closely adjacent each other to form a first wound layer, some of the wires of said first wound layer being formed by said stabilized superconductor assembly; and

a layer of nonsuperconductive wire spirally wound about said first wound layer to form a second wound layer, the direction of spirallying of said second wound layer being opposite to the senses of spiralling of said first wound layer.

2. Superconductor according to claim 1, wherein the good heat-conductive, nonmagnetizable bonding medium (5) comprises a material having a melting temperature not over 320 C.

3. Superconductor according to claim 1, wherein the good heat-conductive, nonmagnetizable bonding medium (5) comprises a material which has an electrical specific resistivity of 1'10 ohm-cm. at maximum at a temperature of4.2 K., and a heat conductivity of at least 0.4 watt/cm.-l(.

4. Superconductor according to claim 1 wherein the pitch of the spiral winding of the superconductor assembly is in the range offrom 1-30 cm./winding.

5. Superconductor according to claim 1, wherein the material of the second wound layer comprises copper wires.

6. Superconductor according to claim 1, wherein said good heat-conductive, nonmagnetizable bonding medium (5) completely encapsulates and bonds both said first and second layers to said support. 

1. Composite superconductor having at least one stabilized superconductor assembly and a hollow, elongated support adapted to have cooling medium circulating therethrough, comprising a plurality of wires spirally wound about said support closely adjacent each other to form a first wound layer, some of the wires of said first wound layer being formed by said stabilized superconductor assembly; and a layer of nonsuperconductive wire spirally wound about said first wound layer to form a second wound layer, the direction of spirallying of said second wound layer being opposite to the senses of spiralling of said first wound layer.
 2. Superconductor according to claim 1, wherein the good heat-conductive, nonmagnetizable bonding medium (5) comprises a material having a melting temperature not over 320* C.
 3. Superconductor according to claim 1, wherein the good heat-conductive, nonmagnetizable bonding medium (5) comprises a material which has an electrical specific resistivity of 1.10 7 ohm-cm. at maximum at a temperature of 4.2* K., and a heat conductivity of at least 0.4 watt/cm..*K.
 4. Superconductor according to claim 1, wherein the pitch of the spiral winding of the superconductor assembly is in the range of from 1-30 cm./winding.
 5. Superconductor according to claim 1, wherein the material of the second wound layer comprises copper wires.
 6. Superconductor according to claim 1, wherein said good heat-conductive, nonmagnetizable bonding medium (5) completely encapsulates and bonds both said first and second layers to said support. 